If there is one accusation that you could never level at either Williams sister, it is that they do not have the guts to get themselves out of a difficult situation. Today it was the turn of Venus Williams to dig herself out of a hole as she saw off Bethanie Mattek-Sands 6-4, 6-2 to reach the third round of the US Open.

The twice former champion has been struggling with reported patellar tendinitis in her left knee and though her movement improved as the match developed, a potential fourth-round clash with Kim Clijsters will tell us a lot more about her title chances.

Mattek-Sands, ranked 124th in the world, gave her some early trouble, and again all eyes were on the heavy strapping Williams wore on her left knee. Having been three points away from defeat in her opening match against the Russian Vera Dushevina, Williams clearly did not want to get involved in many long rallies and her answer was a simple one, hitting herself out of trouble.

In their most recent meeting, at the French Open earlier this summer, Mattek-Sands pushed Williams to a deciding set and she had her moments in the first set. But from 3-3, Williams upped her game to win five of the next six games and she then cruised through the second set to set up a clash with Magdalena Rybarikova of Slovakia.

"I'm not one to complain – everyone has injuries they are dealing with," said Williams. "I will do my best to prepare for the next round. It's going to be a lot of prayer and everything I can throw at it. But I'm tough."

The former world No1 Clijsters, playing in just her third tournament back after two years off the tour and the birth of her first child, today came from a set down to beat Marion Bartoli, the 14th seed, 5-7, 6-1, 6-2. Clijsters also defeated the Frenchwoman – a former Wimbledon runner-up – in the first match of her comeback last month.

Whatever problems Williams may have, they are nothing compared to the travails of Ana Ivanovic who was beaten in the first round on Tuesday night. When the Serbian player won the French Open last summer, becoming world No1 in the process, it seemed like the grand slam titles would mount up, especially after the retirement of Justine Henin.

But whether it was the pressure of being No1 or the greater expectations after winning a grand slam crown, Ivanovic lost her way, changing coaches a couple of times and losing the game that had propelled her to the top. A recent shoulder problem has forced her to curtail her serving motion but even before that, the 21-year-old's serve was misfiring spectacularly and her confidence appears to be shot.

Watching her 2-6, 6-3, 7-6 defeat to the world No52 Kateryna Bondarenka on Tuesday night was a painful experience and the Serb had to fight back the tears a couple of times when she tried to explain what has gone so wrong so quickly.

"It's very disappointing," she said. "It hurts, I can tell you that. I'm sure I will have sleepless nights. But I have to accept it and try to put this year behind me and try to learn from it. I have no doubt I have the potential now to be back in the top."

If anyone is crying out for a sports psychologist it is Ivanovic. Though she can call on the services of the Adidas player development team, which includes Sven Groeneveld and Darren Cahill, she has no full-time coach to confide in. Quite simply, she seems unsure what to do.

"I think I've been thinking about everything too much and trying to address lots of issues with my game," she said. "I feel like I have a plan in place and I know what I have to do in each area of my game but at the moment I think it's a little unbalanced. My fitness is at one level, my mind at another, my game is at another level. I think these all these things have to marry to get into the right direction."